Vehicle safety system with advanced tire monitoring

ABSTRACT

A control system ( 11 ) for a vehicle ( 10 ) includes vehicle dynamics sensors ( 35 - 47 ) providing a vehicle dynamics signal. Tire monitoring system sensors ( 20 ) in each wheel generate tire signals including temperature, pressure and acceleration data. A controller ( 26 ) communicates with the tire monitoring system sensors ( 20 ) and at least one vehicle dynamics sensor, and generates a tire abnormality value as a function of the multi-axis acceleration data of the tire signals. Tire multi-axis acceleration data is also used to detect a roadway departure, and an oversteer or understeer event.

TECHNICAL FIELD

The present invention relates generally to vehicle control systems and tire monitoring systems. More particularly, the present invention is related to vehicle control systems incorporating advanced tire monitoring for improved safety.

BACKGROUND

Tires are an important safety-related component because the tire/road contact patch largely determines the dynamic behavior of the vehicle. For instance, low tire pressure may cause unstable vehicle motion. Tire tread separation may lead to a variety of unstable vehicle motions, such as over-steer or under-steer. Abnormal tire wear may cause untrue driving performance. Tire imbalance can cause tire grip variation and varying stability. Thus, it is desirable to monitor the status of the vehicle tires.

However, most conventional tire monitoring systems only monitor tire pressure. Current tire pressure monitoring sensors have limited functionality, and are not capable of discerning coordinate acceleration data for a wheel. Conventional tire pressure sensors provide pressure and temperature sensing along with data processing and wireless communication of such data. Most also include a movement detection device such as switch or piezoelectric device that activates upon a radial acceleration. The movement detection devices “wake” the sensor to initiate data transmission, while saving battery life while the wheel is not moving.

Advanced tire monitoring sensors (ATMS) are currently being developed. Besides traditional pressure and temperature data, ATMS include coordinate acceleration data for the associated wheel. This is accomplished with micro-electro-mechanical systems (MEMS) accelerometers. Such devices have advantages in terms of robustness, and the ability to provide a linear output response to acceleration. Multiple MEMS are also contemplated to provide multi-axis (coordinate) acceleration data for the associated wheel.

ATMS provide the potential to vehicle manufacturers to offer new or enhanced capabilities in vehicle systems. The present disclosure is directed toward providing improved vehicle safety systems utilizing ATMS.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a safety system for a vehicle including a tire sensor located within each wheel of the vehicle and generating a tire signal comprising pressure, temperature and multi-axis acceleration data. The system also includes at least one vehicle dynamics sensor providing a vehicle dynamics signal, such as the vehicle speed and braking. Further, a controller communicates with the tire sensor and the at least one vehicle dynamics sensor. The controller, in response to the vehicle dynamics signal, generates a tire abnormal state value as a function of the multi-axis acceleration data of the tire signal, and transmits the tire abnormal state value to at least one vehicle system controller. The system controller can be a stability control system.

The controller can generate the tire abnormal state value as a function of the tire signal by comparing frequency response characteristics of the tire signal to stored frequency response characteristics indicative of different tire abnormalities. Alternatively, the controller can generate the tire abnormal state value as a function of the tire signal by comparing frequency response characteristics of one of the tire signals to frequency response characteristics of at least two other tire signals.

In one aspect of the invention, the tire abnormal state value is a loose wheel value. The controller can generate the loose wheel value as a function of the tire signal by comparing amplitude response characteristics of the tire signal to stored amplitude response characteristics indicative of a loose wheel condition. Similarly, the controller can further generate the loose wheel value as a function of the tire signal by comparing frequency response characteristics of one of the tire signals to frequency response characteristics of at least two other tire signals. An indicator can be used for signaling the tire abnormal state value, including the loose wheel value.

In another aspect of the invention, the stability control system is adapted to modify stability control parameters in response to the tire abnormal state value.

Another embodiment of the present invention provides a safety system for a vehicle including a tire sensor located within each wheel of the vehicle and generating a tire signal comprising pressure, temperature and multi-axis acceleration data; and a controller communicating with each tire sensor. The controller generates a roadway departure signal as a function of the multi-axis acceleration data of the tire signals, and transmits the roadway departure signal to at least one vehicle system controller. The controller can generate the roadway departure signal as a function of the tire signals by comparing frequency and amplitude response characteristics of the tire signal to stored frequency and amplitude response characteristics indicative of different roadway surfaces. Alternatively, or additionally, the controller generates the roadway departure signal as a function of the tire signals by comparing frequency response characteristics of the left tire signals to frequency response characteristics of the right tire signals.

In a further aspect of the invention, the at least one vehicle system controller can be a stability control system which is adapted to modify stability control parameters in response to the roadway departure signal.

Yet another embodiment of the present invention provides a safety system for a vehicle including a tire sensor located within each wheel of the vehicle and generating a tire signal comprising pressure, temperature and multi-axis acceleration data; at least one vehicle dynamics sensor providing a vehicle dynamics signal; a brake system for applying a braking torque to each of the vehicle wheels in response to a brake signal; and a controller communicating with the tire sensor and the at least one vehicle dynamics sensor. The controller generates a lateral tire force signal for each of the vehicle wheels as a function of the respective multi-axis acceleration data of the tire signal, and determines an oversteer/understeer signal as a function of the lateral tire force signals. The brake signal to the brake system is generated in response to the oversteer/understeer signal. The controller generates the oversteer signal by detecting a sudden decrease in lateral tire forces for both of the rear tires, in the presence of lateral tire forces in the same direction on the front tires. The controller generates the understeer signal by detecting a sudden decrease in lateral tire forces for both of the front tires, in the presence of lateral tire forces in the same direction on the rear tires. In this example, the vehicle dynamics signal can include a vehicle speed signal and a steering wheel angle signal.

The embodiments of the present invention provide several advantages. One advantage provided by an embodiment of the present invention is a safety control system that is capable of obtaining tire defect knowledge, or roadway departure knowledge and adjusting safety control functions accordingly to improve vehicle safety.

The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention reference should now be had to the embodiments illustrated in greater detail in the accompanying figures and described below by way of examples of the invention wherein:

FIG. 1 is a block diagrammatic and perspective view of a vehicle with variable vectors and coordinate frames in accordance with an embodiment of the present invention;

FIG. 2 is a block diagrammatic view of a tire monitoring system in accordance with an embodiment of the present invention;

FIG. 3 is a block diagrammatic view of a tire sensor according to an embodiment of the present vehicle control system;

FIG. 4 is a block diagrammatic view of a control system, including a tire monitoring system for a vehicle in accordance with an embodiment of the present invention;

FIG. 5 is a logic diagram illustrating a method of operating a control system of a vehicle in accordance with an embodiment of the present invention providing loose wheel detection;

FIG. 6 is a graphical representation of ATMS sensor amplitude-time response data;

FIG. 7 is a graphical representation of ATMS sensor magnitude-frequency response data;

FIG. 8 is a logic flow diagram illustrating a method of detecting a loose wheel in accordance with the method of FIG. 5;

FIG. 9 is a logic diagram illustrating a method of operating a control system of a vehicle in accordance with an embodiment of the present invention providing tire abnormality detection;

FIG. 10 is a logic flow diagram illustrating a method of detecting a tire abnormality in accordance with the method of FIG. 9;

FIG. 11 is a logic diagram illustrating a method of operating a control system of a vehicle in accordance with an embodiment of the present invention providing roadway departure detection;

FIG. 12 is a logic flow diagram illustrating a method of roadway departure detection in accordance with the method of FIG. 11; and

FIG. 13 is a logic diagram illustrating a method of operating a control system of a vehicle in accordance with an embodiment of the present invention providing oversteer/understeer detection.

DETAILED DESCRIPTION

In the following figures, the same reference numerals will be used to identify the same components. The present invention may be used in conjunction with vehicle control systems including a yaw stability control (YSC) system, roll stability control (RSC) system, lateral stability control (LSC) system, integrated stability control (ISC) system, or a total vehicle control system for achieving desired vehicle performance. The present invention is also described with respect to an integrated sensing system (ISS), which uses a centralized motion sensor cluster such as an inertial measurement unit (IMU) and other available, but decentralized, sensors. Although a centralized motion sensor, such as an IMU, is primarily described, the techniques described herein are easily transferable to using the other discrete sensors.

In the following description, various operating parameters and components are described for several constructed embodiments. These specific parameters and components are included as examples and are not meant to be limiting.

Referring to FIG. 1, an automotive vehicle 10 with a control system of the present invention is illustrated with the various forces and moments thereon. Vehicle 10 has front right (FRW) and front left (FLW) wheel/tires 12 a and 12 b and rear right (RRW) wheel/tires 12 c and rear left (RLW) wheel/tires 12 d, respectively. The vehicle 10 may also have a number of different types of front steering systems 14 a and rear steering systems 14 b, including having each of the front and rear wheels 12 a, 12 b, 12 c and 12 d configured with a respective controllable actuator, the front and rear wheels 12 having a conventional type system in which both of the front wheels 12 a, 12 b are controlled together and both of the rear wheels 12 c, 12 d are controlled together, a system having conventional front steering and independently controllable rear steering for each of the wheels 12 c and 12 d, or vice versa. Generally, the vehicle 10 has a weight represented as Mg at the center of gravity of the vehicle 10, where g=9.8 m/s² and M is the total mass of the vehicle 10.

The control system 11 has rollover mitigation and prevention systems, which include and/or comprise of active/semi-active suspension systems, an active steering system, a deployable lateral stability system, inwardly mounted wheel assemblies, and other related devices such as known in the art. The control system 11 may also be used with or include an anti-roll bar, or airbags or other safety devices deployed or activated upon sensing predetermined dynamic conditions of the vehicle 10.

The control system 11 is in communication with a sensing system 16. The sensing system 16 may have many different active and passive sensors including the sensor set typically found in a roll stability control or a rollover control system (including lateral accelerometer, yaw rate sensor, steering angle sensor and wheel speed sensor which are equipped for a traditional yaw stability control system) together with a roll rate sensor and a longitudinal accelerometer. The sensing system 16 may also includes object detection sensors, which aid in the detection of an imminent rollover obstacle. An “imminent rollover obstacle” is an object, such as a curb or other object, having a top surface that is above that of the road surface currently being traveled on. An imminent rollover obstacle is also an object for which there is a high probability of the host vehicle colliding therewith and a high probability that such a collision would cause the vehicle to rollover. When a vehicle is experiencing a large roll angle or high lateral slip angle and comes in contact with an imminent rollover obstacle, a rollover may result. The object creates a pivot point upon which a rollover occurs. The various sensors will be further described below and are shown with respect to FIGS. 2 and 4.

The sensors may also be used by the control system 11 in various determinations such as to determine a lifting event, determine a height and position of a mass, etc. wheel speed sensors can be mounted at each corner of the vehicle and generate signals corresponding to the rotational speed of each wheel. The rest of the sensors of the sensing system 16 may be mounted directly on the center of gravity of the vehicle body, along the directions x, y, and z shown in FIG. 1. As those skilled in the art will recognize, the frame from b₁, b₂, and b₃ is called a body frame 22, whose origin is located at the center of gravity of the car body, with the b₁ corresponding to the x axis pointing forward, b₂ corresponding to the Y axis pointing off the driving side (to the left), and the b₃ corresponding to the z axis pointing upward. The angular rates of the car body are denoted about their respective axes as ω_(x) for the roll rate, ω_(y) for the pitch rate and ω_(z) for the yaw rate. Calculations may take place in an inertial frame 24 that may be derived from the body frame or chassis 22 as described below.

The angular rate sensors and the accelerometers may be mounted on the vehicle car body along the body frame directions b₁, b₂, and b₃ which are the x-y-z axes of the sprung mass of the vehicle.

The longitudinal acceleration sensor is mounted on the car body located at the center of gravity, with its sensing direction along b₁ axis, whose output is denoted as a_(x). The lateral acceleration sensor is mounted on the car body located at the center of gravity, with its sensing direction along b₂ axis, whose output is denoted as a_(y).

FIG. 1 depicts a road frame system r₁r₂r₃ that is fixed on the driven road surface, where the r₃ axis is along the average road normal direction computed from the normal directions of the four-tire/road contact patches.

Referring now to FIG. 2, a block diagrammatic view of an advanced tire monitoring system (ATMS) 18 for a vehicle 10 in accordance with an embodiment of the present invention is shown. The control system 11 communicates with an advanced tire monitoring system 18 and includes a safety control system 25. The safety controller may be a controller for detecting a rollover event, roadway departure, loose wheel condition, abnormal tire condition, or a roadway surface condition. Examples of such safety control systems are described below. The control system 11 utilizes tire status information gathered from the advanced tire monitoring system 18 in operation of the safety control system 25. The ATMS 18 provides tire pressure, air temperature with in the tire and acceleration data to the control system 25. A sample advanced tire monitoring system is described in detail with respect to FIGS. 2 and 3. A sample safety control system is described with respect to FIG. 4. Logic routines for different safety functions are described with respect to FIGS. 5 through 13.

The control system 11 includes one or more controllers. The controllers may be part of the advanced tire monitoring system 18, the safety control system 25, or may be a stand-alone controller. The safety control system 25 may be coupled to other control systems to respond to safety, comfort or convenience events as detected by the logic routines and ATMS 18. Such control systems could include a brake control system that is used to actuate brakes; a suspension control system for activating suspension components to mitigate the effect of a detected event; a steering control system to likewise mitigate a detected event; active and passive safety systems; a central tire inflation system, and the like. Control events related to safety, comfort or convenience may be indicated to a vehicle occupant via an indicator 90.

Several of the stated control systems are shown and described with respect to FIG. 4. Therein, the control system 11 is illustrated in further detail having a controller 26, a passive safety system 27-30, multiple active systems 31-34, various vehicle status sensors, and driver or vehicle operator input sensors 20 and 35-47. The passive system 27 includes object detection devices or sensors 28, collision detection sensors 29, and various passive countermeasures 30. The active systems may include a brake control system 31, a steering control system 32, a suspension control system 33, and a drivetrain control system 34. Based upon inputs from the sensors, the safety control system 25 may operate the safety device 51.

The controllers described herein may be microprocessor based such as a computer having a central processing unit, memory (RAM and/or ROM) and associated input and output buses. The controllers may be application-specific integrated circuits or may be formed of other logic devices known in the art. The controllers may each be a portion of a central vehicle main control unit, an interactive vehicle dynamics module, a restraints control module, a main safety controller, a control circuit having a power supply, combined into a single integrated controller, or may be a stand-alone controller as shown.

Referring again to FIG. 2, the advanced tire monitoring system 18 monitors the air pressure, temperature and multi-axis accelerations for a right front tire 12 a, a left front tire 12 b, a right rear tire 12 c, and a left rear tire 12 d. Each tire 12 a-12 d has a respective ATMS sensor 20 a-20 d, each of which has a respective antenna 19 a-19 d. Each tire 12 a-12 d is positioned upon a corresponding wheel.

A fifth tire or spare tire 12 e is also illustrated having an ATMS sensor 20 e and a respective antenna 19 e. Although five wheels are illustrated, the tire status of various numbers of wheels may be monitored. For example, the present invention applies equally to vehicles such as pickup trucks that have dual wheels for each rear wheel. Also, various numbers of wheels may be used in a heavy duty truck application having dual wheels at a number of locations. Further, the present invention is also applicable to trailers and extra spares.

Each tire 12 may have a respective initiator 23 a-23 e positioned within the wheel wells adjacent to the tire 12. Initiator 23 generates a low frequency RF signal initiator and is used to initiate a response from each wheel so that the position of each wheel may be recognized automatically by the advanced tire monitoring system 18. Initiators 23 are coupled directly to the advanced tire monitoring system 18. In commercial embodiments where the position programming is done manually, the initiators may be eliminated.

The controller comprising the ATMS 18 may be microprocessor based controller having a programmable CPU that may be programmed to perform various functions and processes including those set forth herein. Controller has a memory 18 a associated therewith. Memory 18 a may be various types of memory including ROM or RAM. The memory is used to store various thresholds, calibrations, tire characteristics, wheel characteristics, serial numbers, conversion factors, temperature probes, spare tire operating parameters, and other values needed in the calculation, calibration and operation of the advanced tire monitoring system 18. For example, memory may contain a table that includes the sensor identification. Also, the warning status of each of the tires may also be stored within the table.

The ATMS 18 is also coupled to a transceiver 80. Although the transceiver 80 is illustrated as a separate component, the transceiver 80 may also be included within ATMS 18. The transceiver 80 has an antenna associated therewith. The antenna is used to receive pressure, temperature and multi axis acceleration information from ATMS sensors 20 a-20 e. One transceiver may be used for all of the ATMS sensors 20, or a front and rear transceiver may be used, or dedicated transceivers may be used, each in communication with the ATMS 18. The ATMS 18 performs preprocessing before placing the tire data on the vehicle communications bus (CAN) or other digital protocol for transmission to the safety control system 25.

In the example shown, the safety control system 25 is also coupled to a plurality of sensors 81 and other measurement and control systems such as an IMU 82. The sensors 81 may include a barometric pressure sensor, an ambient temperature sensor, an object detection sensor, a speed sensor, a brake pedal sensor, a throttle position sensor, steering wheel position sensor, and an ignition sensor. Sensor data may also be provided such as suspension position and loading. Of course, various other types of sensors may be used. A barometric pressure sensor generates a barometric pressure signal corresponding to the ambient barometric pressure. Thus, barometric pressure compensation may be used, but is not required in the calculation for determining the pressure within each tire 12. The ambient temperature signal corresponding to the ambient temperature and may also be used to generate a temperature compensated pressure profile. The sensor data 81 may also be preprocessed before being communicated to the safety control system 25.

The inertial measurement unit (IMU) 82 contains inertial sensors for detecting vehicle yaw, pitch and roll. This data is communicated to the safety control system 25 in order to determine whether a rollover event exists. This data can also act to initiate the ATMS 18 when a potential for rollover exists, or indicate that data collection from the ATMS sensors 20 is desirable.

Safety, comfort and convenience devices are generally indicated at 51. Safety devices may include restraints components such as seat mounted side airbags or side curtain airbags, seat belt pretensioners, deployable trim panels and the like. To prevent or mitigate a rollover event, safety devices 51 may also include vehicle lateral support systems, wheel sets or active suspension components. Further safety devices 51 may include suspension components such as active bushings or linkages and, pneumatic or hydraulic cylinders. They may also include a centralize tire inflator for changing the amount of tire pressure at each of the tires 12.

Control system 25 may also be coupled to an indicator 90. The indicator 90 may include a video system, an audio indicator, a heads-up display, a flat-panel display, a telematic system, a dashboard indicator, a panel indicator, or other indicator known in the art. In one embodiment of the present invention, the indicator 90 is in the form of a heads-up display and the indication signal is a virtual image projected to appear forward of the vehicle 10. The indicator 90 provides a real-time image of the target area to increase the visibility of the objects during relatively low visible light level conditions without having to refocus ones eyes to monitor an indication device within the vehicle 10. Indicator 90 may provide some indication as to the operability of the system such as confirming receipt of a signal such as a calibration signal or other commands, warnings, and controls. Indicator 90 may also alert the vehicle operator with respect to tire pressure data, a safety event, or a comfort or convenience event.

Referring now also to FIG. 3, a schematic view of an advanced tire monitoring system (ATMS) sensor 20 in accordance with an embodiment of the present invention is shown. The ATMS sensor 20 is illustrated mounted to a rim of a vehicle wheel 12 inside the tire. The sensor has a transmitter/receiver or transceiver 83. The transmitter/receiver 83 is coupled to antenna 19 for transmitting information to transceiver 80. The transmitter/receiver 83 may be used to receive an activation signal from an initiator 23 located at each wheel, if an initiator is used in the particular application. The sensor circuit 20 may have various information such as a serial number memory 84, a pressure sensor 85 for determining the pressure within the tire, a temperature sensor 86 for determining the temperature within the tire, and a motion detector in the form of a multi-axis accelerometer 87. Preferably, the accelerometer 87 is a MEMS device. The accelerometer may be used to activate the advanced sensing system. The initial message is referred to as a “wake” message, meaning the sensor sensing circuit is now activated to send its pressure transmissions and the other data.

Each of the transceiver 83, memory 84, pressure sensor 85, temperature sensor 86, and motion sensor 87 are coupled to a power source such as a battery 88. The battery 88 may be a long-life battery capable of lasting the life of the tires. In another aspect, the battery may be omitted, or have a substantially smaller capacity. An energy scheme using an RF field generated by an antenna on the vehicle, such as antenna 181, can be used to power the sensor circuit 20. This is generally indicated in FIG. 3 by the RF signal path in both sensor circuit 20 and transceiver circuit 80. A self-generating energy scheme may also be used wherein the device 20 scavenges energy from the rotational movement of the tires. Such schemes may permit continuous sensor data transmission and/or longer sensor life when equipped with a battery supply.

A sensor function monitor 89 in the form of a microcontroller core or state machine, for example, may also be incorporated into ATMS sensor circuit 20. The sensor function monitor 89 generates an error signal when various portions of the ATMS circuit are not operating or are operating incorrectly. Also, sensor function monitor may generate a signal indicating that the circuit is operating normally. The ATES function monitor microcontroller 89 can locally pre-process the sensor data streams prior to wireless delivery to the vehicle transceiver. It also provides a supervisory function to control the overall operation of the sensor including processing, diagnostics and error detection.

The transceiver 80 in communication with the ATMS sensor 20, similarly includes a power source, transmitter/receiver device, microcontroller and antenna. It also includes an interface for the vehicle communications bus (CAN bus). Thus, each ATMS sensor 20 communicates wirelessly with the controller 18 for at least a portion of its communication path. The transceiver 80 receives either the raw sensor data or the pre-processed sensor data from the tire sensors and communicates with the ATMS 18 for further processing with defined algorithms.

An advantage of the ATMS sensors 20 just described is that it provides temperature and pressure data for each tire, as well as x, y and z acceleration data for each tire. This acceleration data is generated much more directly than vehicle acceleration data generated by conventional IMU sensing systems. Traditional IMU systems determine roll, pitch and yaw data above the vehicle suspension. Thus, signal propagation is delayed and/or modified with other stimuli and transfer functions because of the distance of the signal source, i.e., what is occurring at the contact patches of the tires or to the tires themselves. The ATMS sensors 20 of the present invention reduce the signal propagation path and latency because they are distributed very close to the road surface and other inputs, such as objects impacting the tires. The ATMS sensors 20 allow data signals directly from the relevant tire/wheel. Items such as road surface characteristics, impacts and/or obstacles, tire defects, wheel defects and suspension defects can all be monitored by signature analysis of the wheel data provided by the ATMS sensors 20.

Referring to FIG. 4, a block diagrammatic view of a safety control system 25 in accordance with an embodiment of the present invention is shown. The safety control system 25 may consist of a rollover stability controller RSC 56. In this example, the safety control system 25 monitors many sensor inputs, including inputs from ATMS sensors 20 located at each wheel/tire of the vehicle. Front right (FR) and front left (FL) wheel/tires 12 a and 12 b and rear right (RR) wheel/tires 12 c and rear left (RB) wheel/tires 12 d, respectively, are shown and may be part of a vehicle, such as the vehicle 10. The vehicle may also have a number of different types of front steering systems and rear steering systems, including having each of the front and rear wheels configured with a respective controllable actuator, the front and rear wheels having a conventional type system in which both of the front wheels are controlled together and both of The rear wheels are controlled together, or a system having conventional front steering and Independently controllable rear steering for each of the wheels or vice versa.

The safety control system 25 includes the controller or integrated sensing system (ISS) 26, which signals the safety device 51, the suspension control 49, the engine/transmission controller 123 and the brake controller 60 in response to information received from the ATMS 18, and the sensor cluster 50. In other application, as described below, the TSS 26 may only indicate to the vehicle operator a sensed condition, without taking any other active measures to alter the sensed condition.

The controller 26 as well as the suspension control 49, the brake controller 60, and the engine/transmission controller 123 may be microprocessor based such as a computer having a central processing unit, memory (RAM and/or ROM), and associated input and output buses. The controllers 26, 49, 60, and 123 may be application-specific integrated circuits or may be formed of other logic devices known in the art. The controllers 26, 49, 60, and 123 may each be a portion of a central vehicle main control unit, an interactive vehicle dynamics module, a restraints control module, a main safety controller, a control circuit having a power supply, combined into a single integrated controller, or may be a stand-alone controller as shown. The controllers 26, 49, 60, and 123 may be configured to be mounted and located within a vehicle dashboard or vehicle panel or in some other location on the vehicle 10.

The controllers and devices in communication with the ISS 26 are described below. Thereafter, the inputs to the ISS 26 are described.

Referring to FIG. 4, a passive safety system may be in communication with the controller or ISS 26. The passive safety system 27 includes collision detection sensors 29, object detection sensors 28, and passive countermeasures 30. The object detection sensors 28 monitor the environment around the vehicle 10 and generate object detection signals upon detection of an object. The object detection sensors 28 may be infrared, visible, ultrasonic, radar, active electro magnetic wave-ranging, or lidar based, a charged-coupled device, a series of photodiodes, or in some other form known in the art. Wave-ranging devices may include radar, lidar, stereo camera pairs, 3-D imagers, with active infrared illumination, or other wave-ranging devices known in the art. Vision sensors may refer to robotic cameras or other visual imaging cameras. The wave ranging sensors and the vision sensors may be monocular or binocular and may be used to obtain height, width, depth, range, range rate, angle, and any other visual aspect information. Monocular cameras may be used to obtain less accurate and less reliable range and range rate data as compared to binocular cameras. The object detection sensors 28 may also be in the form of an object indicator. The object detection sensors 28 may be in various locations on the vehicle and any number of each may be utilized. The object detection sensors may also include occupant classification sensors (not shown). With respect to tripped rollover events, object detection sensors 28 detect objects which may cause a tripped rollover.

The collision detection sensors 29 are used to detect a collision and more particularly, a side collision. The collision detection sensors 29 may also be located anywhere on the vehicle 10 and generate collision detection signals in response to a collision. The collision detection sensors 29 may include sensors that are used as vehicle status sensors, such as the yaw rate sensor 35, the lateral acceleration sensor 39, and the longitudinal acceleration sensor 40. The collision detection sensors 29 may also be in the form of an accelerometer, a piezoelectric sensor, a piezo-resistive sensor, a pressure sensor, a contact sensor, a strain gage, or may be in some other form known in the art.

The passive countermeasures 30 may include internal air bag control, seatbelt control, knee bolster control, head restraint control, load limiting pedal control, load limiting steering control, seatbelt pretensioner control, external air bag control, pedestrian protection control, and other passive countermeasures known in the art. Air bag control may include control over front, side, curtain, hood, dash, or other type of airbags known in the art. Pedestrian protection may include a deployable vehicle hood, a bumper system, or other pedestrian protective devices.

The brake control system 31 can also be in communication with the controller 26. The brake control system 31 includes the brake controller 60 that actuates front vehicle brakes 62 a and 62 b and rear vehicle brakes 62 c and 62 d. The vehicle brakes 62 are associated with the wheels 12 a-12 d. The brakes 62 may be independently actuatable through the brake controller 60. The brake controller 60 may control the hydraulic system of the vehicle 10. Of course, electrically actuatable brakes may be used in the present invention. The brake controller 60 may also be in communication with other safety systems such as an antilock brake system 64, a yaw stability control system 66 and a traction control system 68.

The steering control system 32, which may also communicate with the controller 26, can include a number of different types of front and rear steering systems including having each of the front and rear wheels 12 a-12 d configured with respective controllable adjusting elements 55A-D. The wheels 12 may be controlled together or individually. The safety controller 26 may control the position of the front right wheel adjusting element 55A, the front left wheel adjusting element 55B, the rear left wheel adjusting element 55D, and the right rear wheel adjusting element 55C. Although as described above, two or more of the adjusting elements may be simultaneously controlled. For example, in a rack-and-pinion system, the two wheels coupled thereto are simultaneously controlled. Based on the inputs from sensors 35-47 and from the ATMS 18, the safety controller 26 controls the steering position and/or braking of the wheels. With respect to the steering control system 32, the adjusting elements permit directional control of the particular wheel.

The controller 26 may also communicate with the suspension control system 33. The suspension control system 33 includes the suspension control 49, the suspension 48, and the suspension adjusting elements 55A-55D (FR_(SP), FL_(SP), RR_(SP), RL_(SP)) that are associated with each wheel 12. The suspension control 49 and adjusting elements 55A-55D may be used to adjust the suspension 48 to prevent rollover. The adjusting elements 55A-55D may include electrically, mechanically, pneumatically, and/or hydraulically operated actuators, adjustable dampers, or other known adjustment devices, and are described below in the form of actuators. The adjusting elements 55 may allow for active modification of the suspension response or geometry. For example, they may comprise active dampers. The adjusting elements 55 may also be bushings which can electronically decouple the sway bar associated with a wheel to enhance suspension articulation. Another example is a bushing comprising magnetorheological fluid and oil allowing it to articulate within the wheel joint to alter suspension geometry and/or the wheel's NVH characteristics. In a further example, the suspension components 55 may be pneumatic cylinders for adjusting the ride height of the vehicle. The suspension control system 33 may also operate to adjust the tire pressure with central tire inflation capability. For instance, the tire pressure may be lowered to traverse softer road conditions. This feature can be used in response to a road surface characteristic detection as described below, or a low tire pressure signal.

The controller 26 may also be in communication with the drivetrain control system 34. The drivetrain control system 34 includes an internal combustion engine 120 or other engine known in the art. The engine 120 may have a throttle device 142 coupled thereto, which is actuated by a foot pedal 144. The throttle device 142 may be part of a drive-by-wire system or by a direct mechanical linkage between the pedal 144 and the throttle device 142. The engine controller 123 may be an independent controller or part of the controller 26. The engine controller 123 may be used to reduce or increase the engine power. While a conventional internal combustion engine is contemplated, the vehicle 10 could also be powered by a diesel engine or an electric engine or the vehicle could be a hybrid vehicle utilizing two or more types of power systems.

The drivetrain system 34 also includes a transmission 122, which is coupled to the engine 120. The transmission 122 may be an automatic transmission or a manual transmission. A gear selector 150 is used to select the various gears of the transmission 122. The gear selector 150 may be a shift lever used to select park, reverse, neutral, and drive positions of an automatic transmission. Of course, in the case of electric vehicles, electric motors may replace the conventional engine/transmission setup shown in this example.

Safety device 51 may control one or more passive safety countermeasures such as airbags 30 or a steering actuator 55A-D at one or more of the wheels 12 a, 12 b, 12 c, 12 d of the vehicle. The safety device 51 may also operate the suspension control/tire inflator 49 as described above.

A lateral support system 70 may also be in communication with the safety controller 26, either directly or through the safety device 51. The lateral support system 70 is adapted to mitigate tripped rollover events. It can include a deployable set of linkages and one or more arms, which each have a wheel set attached to the outwardly extending end thereof. The inward end of the arm is attached to a deploying mechanism. In normal driving conditions the wheels sets are not in contact with the driving surface. The lateral support system 70 may also or alternatively include laterally deployable airbags. The airbags are also outwardly deployed to prevent or mitigate a tripped rollover. The airbags may be deployed from any location on the vehicle 10 and any number of airbags may be utilized.

Indicator 90 may also be in communication with the controller 26 directly, or indirectly though the safety device 51. It may be used to indicate to a vehicle operator various vehicle-related and status information

The controller 26 receives numerous inputs to aide in determining vehicle dynamic conditions. For example, it may determine whether a rollover event is in progress or is imminent. The controller 26 may include a signal multiplexer 50 that receives the signals from the sensors 20 and 35-47. In this example, the signal multiplexer 50 provides the signals to a roll stability control (RSC) feedback control command 56 which is part of the safety controller 25.

The controller 26 takes advantage of the information provided by the advanced tire monitoring sensors 20 described above, as well as the traditional vehicle dynamics sensors 35-47 in monitoring for potential rollover events and other vehicle and roadway dynamics. Thus, the multi-axis acceleration data, temperature data and pressure data for each wheel is analyzed in various safety schemes described in further detail with respect to FIGS. 5 through 13. Heretofore, control systems have not considered coordinate acceleration data at each wheel. Rather, such vehicle and roadway data was only determined by means such as conventional IMU units, typically with reference to the body center frame, and located above the suspension line of the vehicle.

Briefly, the vehicle status sensors 35-47 may include the yaw rate sensor 35, the pitch rate sensor 36, the roll rate sensor 37, the vertical acceleration sensor 38, lateral acceleration sensor 39, longitudinal acceleration sensor 40, the speed sensor 41, the steering wheel angle velocity sensor 42, the steering angle (of the wheels or actuator) position sensor 43, the suspension load sensor 44, the suspension position sensor 45, the accelerator/throttle signal generator 46, and the brake pedal/brake signal generator 47. It should be noted that various combinations and sub-combinations of the sensors may be used. The steering wheel angle sensor 42, the accelerator/throttle signal generator 46, and the brake pedal/brake signal generator 47 are considered driver input sensors, since they are associated with a pedal, a wheel, or some other driver input device. Depending on the desired sensitivity of the system and various other factors, not all the sensors 35-47 may be used in a commercial embodiment. These sensors may be used in a conventional rollover stability control scheme, if the vehicle is so equipped, as in this example. One example of a rollover stability control scheme using such sensors, as well as an ATMS 18 is disclosed in U.S. patent application Ser. No. 11/693,131, which is incorporated by reference herein. In the safety schemes discussed below, however, the control method is based on feedback from the ATMS 18 alone, or in combination with only one or a few other sensor inputs such as the driver inputs and vehicle speed. Thus, the remaining sensors 35-47 are only included for completeness, and may only act as confirmatory sensors to the detected condition based on the ATMS 18 data.

The vehicle dynamic sensors 35-40 may be located at the center of gravity of the vehicle 10. Those skilled in the art will recognize that the sensors may also be located off the center of gravity and translated equivalently thereto.

FIG. 5 is a logic flow diagram illustrating a method of operating a control system of a vehicle in accordance with an embodiment of the present invention providing loose wheel detection. Although the following steps are described primarily with respect to the embodiments of FIGS. 1-4, they may be modified and applied to other embodiments of the present invention, including vehicle embodiments wherein less than all sensors 35-47 are included. Indeed, in this example, only an ATMS sensor 20 at each wheel is analyzed.

In general terms, the loose wheel detection scheme relies upon a detectable shift in a wheel's vibration characteristics as sensed by the ATMS sensor 20 at the wheel. Such conditions as an inadequately tightened lug nut will manifest as detectable vibrations. The method can detect a loose wheel individually by comparing the sensed acceleration data for a wheel to a stored wheel acceleration signature, or by comparing data for the wheel under consideration to data for the other vehicle wheels. Combining these two approaches improves the robustness of the system.

Referring to FIG. 5, in step 200, tire signals are generated, which are indicative of the current tire pressure, temperature and multi-axis acceleration within each tire of the vehicle. This information is provided by the advanced tire monitoring system sensors 20. Steps 202, 204 and 206 preprocess the data generated by the ATMS sensors 20. In block 202 the data is segmented and parsed into discrete time windows and transformed from the time domain into the frequency domain using the Fourier Transform (FT) techniques. Alternate embodiments may use other frequency transformation techniques such as wavelet transformation techniques to transform the time domain data into its frequency domain representation. In block 206 the signal amplitude-time data is parsed into discrete time windows and signal amplitude vs. time table is generated for each time window for each of the sensor data as shown in FIG. 6. The generated tables are used in the subsequent algorithm blocks and are compared to known stored loose wheel conditions tables to determine the current loose wheel conditions. In block 204 a signal magnitude vs. frequency table is generated for each time window as shown in FIG. 7. The generated tables are used in the subsequent algorithm blocks and are compared to known stored loose wheel conditions tables to determine the loose wheel conditions. As mentioned above, because the data is generated inside each tire for the vehicle, the signature profiles of the sensor data provide direct insight into what each tire is experiencing while it contacts the road surface. This data is generated much more directly than vehicle acceleration data generated by conventional IMU sensing systems because traditional IMU systems determine roll, pitch and yaw and coordinate accelerations above the vehicle suspension. The ATMS sensors 20 eliminate signal propagation through the suspension, and provide a clearer “view” of the vehicle dynamics.

The preprocessed ATMS sensor data is then analyzed according to loose wheel detection criteria in step 208. A more detailed explanation of the loose wheel detection criteria is provided in the example of FIG. 8. In this example, the sensor signals are compared to stored sensor frequency response signatures from block 209, and stored amplitude/time response signatures from block 210.

If a loose wheel is detected in step 212, a loose wheel fault condition is set in block 214 and an indicator can be modified in block 216 to alert the vehicle operator. The control system may indicate that a wheel is loose and the extent thereof. This information may also be stored, viewed, and downloaded for future review and/or evaluation. The viewing and downloading may be to an offboard or offsite system. The control system may also indicate to a vehicle operator that active tasks are being performed and the status of the vehicle. This indicated information may also be stored, viewed, and downloaded for future review and/or evaluation. The viewing and downloading may be to an offboard or offsite system.

The loose wheel condition is then broadcast to other vehicle subsystems in step 218. This may include safety modules such as the active/passive safety systems, ABS, RSC, or integrated vehicle dynamics controller. By broadcasting the loose wheel condition, these other systems can then optimize their performance based upon the loose wheel. For instance, if a rollover event is declared, the thresholds that are used in activating or initiating interventions may be adjusted, scaled, opened, or relaxed, to alter intervention timing because of the loose wheel. In such situations, earlier interventions may be desired. In another example of broadcasting, a pre-arm signal for safety-related countermeasures based upon the tire data may be generated. Pre-arming would be appropriate for the roll stability control system as well as the restraints control system. The brake pressure applied during any intervention or countermeasure may also be modified as a result of the loose wheel detection-particularly at the wheel under consideration. For instance, the brake pressure may be tiered based on the severity of the loose wheel condition: full range or maximum tire pressure range, a reduced range or brake pressure limiting range, and an inactive range or brake pressure prevented range. When the magnitude of the loose wheel condition is estimated to be very low or less than or equal to a first threshold value, the control system may apply a brake pressure up to a maximum threshold. In those cases, the full range brake control functions are maintained. When the magnitude of the loose wheel condition is in a reduced range or between a first threshold LW1 and a second threshold LW2, the control system may apply a reduced or limited brake pressure, which is less than that which would normally be applied. In the reduced range the amount that the brake pressure is limited is gradually or progressively increased. This increase may be linear, may be non-linear, or may result using some other relationship. When the magnitude of the loose wheel condition is greater than or equal to the second threshold LW2, the control system is prevented from applying brake pressure at that wheel. Although the control system is prevented from applying a brake pressure, brake pressure may be applied manually by a vehicle operator. In another embodiment, the control system can override the manual brakes and limits or prevents manual brake pressure to the loose wheel.

The above tasks may be performed via any one or more of the herein mentioned controllers, control systems, stability control systems, or the like. The above-described steps are meant to be illustrative examples; the steps may be performed sequentially, synchronously, simultaneously, or in a different order depending upon the application.

Referring now to FIG. 8, a logic flow diagram illustrating one particular method of wheel sensor-based loose wheel detection in accordance with an embodiment of the present invention is shown. This process is one example of the loose wheel detection as called for in step 208 of FIG. 5. Of course, this example may be modified and applied to other embodiments of the present invention.

The routine starts at steps 220 and 222 by determining whether the vehicle is moving or braking. If the vehicle is moving, but not braking, the logic continues. Otherwise, no loose wheel condition is declared in step 224.

The sensed tire data from steps 202 and 204 as described above, is then compared to stored values from information block 209 in step 226. The stored Fourier response may comprise a lookup table of sensor signatures, each indicative of a loose wheel condition at various speeds. If the current frequency response characteristic matches any stored frequency response characteristic at the same vehicle speed indicative of a particular loose wheel condition in step 228, the logic declares a loose wheel in step 230. Otherwise, no loose wheel condition is declared in step 224. Alternatively, or additionally, step 226 may comprise Fourier response signatures of the other vehicle wheels. In such a case, a deviation, rather than a match, indicative of a loose wheel determines whether a loose wheel condition is satisfied.

In a similar way, the sensed tire data from step 206 in the form of current continuous lateral acceleration data 231 for the wheel, is compared to stored values at the same speed from information block 210 in step 232. If the magnitude of the Y acceleration component exceeds a threshold value in step 232, and the Y component is substantially equal in both the positive and negative directions in step 234, a loose wheel is declared. Step 234 minimizes inadvertent loose wheel detection due to events such as minor tire side impacts. Otherwise, no loose wheel is declared in step 224. Again, the threshold value may be a stored value, or may be derived from the other vehicle wheel data, or both.

FIG. 9 is a logic flow diagram illustrating a method of operating a control system of a vehicle in accordance with an embodiment of the present invention providing tire abnormality detection. Although the following steps are described primarily with respect to the embodiments of FIGS. 1-4, they may be modified and applied to other embodiments of the present invention, including vehicle embodiments wherein less than all sensors 35-47 are included. Indeed, in this example, only an ATMS sensor 20 data at each wheel and the vehicle speed data are analyzed.

In general terms, the tire abnormality scheme detects changes in pressure waves created by the tire tread deformation. Such abnormalities can be declared through pattern recognition using acceleration data profiles stored in memory and/or by comparing the pressure profile of the particular tire to that of the other vehicle tires. Tire abnormalities exhibit higher acceleration signal and spectral content, i.e., acceleration frequency components, in the X, Y and Z axis compared to round and balanced tires. On this basis, tire abnormalities can be detected. A foreign object striking the tire can act as an initiator for the abnormality check. This would be detected by the system as an impulse lateral or vertical acceleration signal.

In response to a detected tire abnormality, suspension or tire adjustments can be made to improve vehicle ride and handling. Adjustments to the suspension contemplated include modifying suspension dampers, ride height, and activating suspension bushings to modify suspension geometry and characteristics at the wheels. Other active suspension components include sway bars that can be electronically decoupled by bushings to provide enhanced suspension articulation. Such features could also be used to automatically correct wheel misalignment, which could also be sensed by the ATMS 18. These suspension components may be used to mitigate the effects of a tire abnormality until the tire can be fixed or replaced.

Referring to FIG. 9, in step 300, tire signals are generated, which are indicative of the current tire pressure, temperature and multi-axis acceleration within each tire of the vehicle. This information is provided by the advanced tire monitoring system sensors 20. Steps 302, 304 and 306 preprocess the data generated by the ATMS sensors 20.

The preprocessed tire sensor data is then analyzed according to tire abnormality detection criteria in step 308. A more detailed explanation of the tire abnormality detection criteria is provided in the example of FIG. 10. In this example, the sensor signals are compared to stored sensor frequency response signatures from block 309.

If a tire abnormality is detected in step 312, a tire abnormality fault condition is set in block 314 and an indicator can be modified in block 316 to alert the vehicle operator. The control system may indicate that a tire is defective. This information may also be stored, viewed, and downloaded for future review and/or evaluation. The viewing and downloading may be to an offboard or offsite system. The control system may also indicate to a vehicle operator that active tasks are being performed and the status of the vehicle. This indicated information may also be stored, viewed, and downloaded for future review and/or evaluation. The viewing and downloading may be to an offboard or offsite system.

The tire abnormality condition is then broadcast to other vehicle subsystems in step 318. This may include safety modules such as the active/passive safety systems, ABS, RSC, or integrated vehicle dynamics controller. By broadcasting the tire abnormality condition, these other systems can then optimize their performance based upon the tire abnormality. For instance, if a rollover event is declared, the thresholds that are used in activating or initiating interventions may be adjusted, scaled, opened, or relaxed, to alter intervention timing because of the tire abnormality. In such situations, earlier interventions may be desired. In another example of broadcasting, a pre-arm signal for safety-related countermeasures based upon the tire data may be generated. Pre-arming would be appropriate for the roll stability control system as well as the restraints control system. The brake pressure applied during any intervention or countermeasure may also be modified as a result of the tire abnormality detection—particularly at the wheel under consideration—as described above with regard to FIG. 5.

The above tasks may be performed via any one or more of the herein mentioned controllers, control systems, stability control systems, or the like. The above-described steps are meant to be illustrative examples; the steps may be performed sequentially, synchronously, simultaneously, or in a different order depending upon the application.

Referring now to FIG. 10, a logic flow diagram illustrating one particular method of wheel sensor-based tire abnormality detection in accordance with an embodiment of the present invention is shown. This process is one example of the tire abnormality detection as called for in step 308 of FIG. 9. Of course, this example may be modified and applied to other embodiments of the present invention.

The routine starts at steps 320 and 322 by determining whether the vehicle is moving or braking. If the vehicle is moving, but not braking, the logic continues. Otherwise, no tire abnormality condition is declared in step 324.

The sensed tire data from steps 302 and 304 as described above, is then compared to stored values from information block 309 in step 326. The stored Fourier response may comprise a lookup table of sensor signatures at various speeds, each indicative of a tire abnormality condition. If the current frequency response characteristic matches any stored frequency response characteristic at the same vehicle speed indicative of a particular tire abnormality condition in step 328, the logic declares a tire abnormality in step 330. Otherwise, no tire abnormality condition is declared in step 324. Alternatively, or additionally, step 326 may comprise comparisons with Fourier response signatures of the other vehicle wheels. In such a case, a deviation, rather than a match, indicative of a tire abnormality determines whether a tire abnormality condition is satisfied.

FIG. 11 is a logic flow diagram illustrating a method of operating a control system of a vehicle in accordance with an embodiment of the present invention providing road departure warning. Although the following steps are described primarily with respect to the embodiments of FIGS. 1-4, they may be modified and applied to other embodiments of the present invention, including vehicle embodiments wherein less than all sensors 35-47 are included.

In general terms, for vehicles which do not have a vision-based road departure warning system, the ATMS-based method described herein can provide road departure warning without any additional hardware. For vehicles with vision-based systems, it can act as a confirmation system. The fact that a tire has left the road surface can be detected by the ATMS alone, using two methods. The first is the detection of vertical acceleration imparted on a tire when it leaves the road surface. The can be detected by performing transient pulse analysis of vertical acceleration between the four tires. The acceleration can also be compared to a characteristic acceleration profile obtained through vehicle testing and stored in electronic memory. The stored signature would be indicative of a tire leaving the road surface. The second method compares the rolling acceleration values, both in the time and frequency domain, to the previous values obtained on the road surface. Since the acceleration profile over time varies depending on the road surface, a change in the acceleration profile indicates that the tire is no longer traveling on that road surface. The time history of the tire's acceleration profile can also be compared with the other tires on the vehicle to indicate that one or more tires are contacting a different surface. Combining these two approaches improves the robustness of the system. This data can be further complemented by determined road friction estimations.

Referring to FIG. 11, in step 400, tire signals are generated, which are indicative of the current tire pressure, temperature and multi-axis acceleration within each tire of the vehicle. This information is provided by the advanced tire monitoring system sensors 20. Steps 402, 404 and 406 preprocess the data generated by the ATMS sensors 20.

The preprocessed tire sensor data is then analyzed according to roadway departure detection criteria in step 408. A more detailed explanation of the roadway departure detection criteria is provided in the example of FIG. 12. In this example, the sensor signals are compared to stored sensor frequency response signatures from block 409.

If a roadway departure is detected in step 412, a roadway departure condition is set and an indicator can be modified in block 416 to alert the vehicle operator. The control system may indicate a roadway departure and the extent thereof. This information may also be stored, viewed, and downloaded for future review and/or evaluation. The viewing and downloading may be to an offboard or offsite system. The control system may also indicate to a vehicle operator that active tasks are being performed and the status of the vehicle. This indicated information may also be stored, viewed, and downloaded for future review and/or evaluation. The viewing and downloading may be to an offboard or offsite system.

The roadway departure condition is then broadcast to other vehicle subsystems in step 418. This may include safety modules such as the active/passive safety systems, ABS, RSC, or integrated vehicle dynamics controller. By broadcasting the roadway departure condition, these other systems can then optimize their performance based upon the roadway departure. For instance, if a rollover event is declared, the thresholds that are used in activating or initiating interventions may be adjusted, scaled, opened, or relaxed, to alter intervention timing because of the roadway departure. In such situations, earlier interventions may be desired. In another example of broadcasting, a pre-arm signal for safety-related countermeasures based upon the ATMS data may be generated. Pre-arming would be appropriate for the roll stability control system as well as the restraints control system. The brake pressure applied during any intervention or countermeasure may also be modified as a result of the roadway departure, as discussed above with regard to FIG. 5.

The above tasks may be performed via any one or more of the herein mentioned controllers, control systems, stability control systems, or the like. The above-described steps are meant to be illustrative examples; the steps may be performed sequentially, synchronously, simultaneously, or in a different order depending upon the application.

Referring now to FIG. 12, a logic flow diagram illustrating one particular method of ATMS sensor-based roadway departure detection in accordance with an embodiment of the present invention is shown. This process is one example of the roadway departure detection as called for in step 408 of FIG. 11. Of course, this example may be modified and applied to other embodiments of the present invention.

The routine starts at steps 420 and 422 by determining whether the vehicle is moving or braking. If the vehicle is moving, but not braking, the logic continues. Otherwise, no roadway departure condition is declared in step 424.

The sensed tire data from steps 402 and 404 as described above, is then compared to stored values from information block 409 in step 426. The stored Fourier response may comprise a lookup table of sensor signatures at various speeds, each indicative of a roadway departure condition. If the current frequency response characteristic matches any stored frequency response characteristic at the same vehicle speed indicative of a roadway departure condition in step 42S, the logic declares a roadway departure in step 430. Otherwise, no roadway departure condition is declared in step 424. In this example, two road surface acceleration profiles are stored and compared to the sensed tire data. In step 42S, the sensed data is compared to stored profiles indicative of roadside “rumble strips”. In step 432, the sensed data is compared to stored profiles indicative of gravel/dirt which may indicate the shoulder of the road adjacent a paved surface. If the profile for gravel/dirt does not match the sensed tire data in step 432, no roadway departure condition is indicated. Otherwise, step 434 determines whether the gravel/dirt profile is being experienced by both the left and right vehicle wheels. If they are the same, it indicates that the entire vehicle is likely traveling on a gravel/dirt road. If only one side of the vehicle is matched to the gravel/dirt profile, however, it is declared a roadway departure. In the event of a declared roadway departure, the driver can be warned as in step 416, and other systems can be alerted in step 418 and pre-armed in step 417, if desirable.

Alternatively, or additionally, steps 428 and 432 may comprise a comparison of the sensed acceleration response for each tire with road surface condition data which is also determined from the ATMS. One example of roadway road surface condition estimation is described in U.S. patent application Ser. No. 11/693,175, which is incorporated by reference herein.

Roadway surface conditions are differentiated by an analysis of the tire acceleration signals provided by the ATMS sensor 20 at each wheel. Rough road surfaces such as dirt roads exhibit higher acceleration signal and spectral content, i.e., acceleration frequency components, in the X and Z axis as compared to smooth road surfaces such as asphalt roads. On this basis, roadway surfaces can be detected for the left and right side vehicle wheels and, correspondingly, a roadway departure can be determined. Other road surface conditions can also be discerned such as ice, water, gravel, snow, etc.

FIG. 13 is a logic flow diagram illustrating a method of operating a control system of a vehicle in accordance with an embodiment of the present invention providing oversteer/understeer warning. Although the following steps are described primarily with respect to the embodiments of FIGS. 1-4, they may be modified and applied to other embodiments of the present invention, including vehicle embodiments wherein less than all sensors 35-47 are included.

Oversteer is a condition whereby, while executing a turn, the lateral forces exerted by rear tires exceed the frictional forces from the road surface and fail to follow the trajectory of the front tires; instead swinging to the outside of the turning direction. Understeer is the analogous situation whereby the lateral forces exerted by the front tires exceed the frictional forces from the road surface and fail to follow the angle indicated by their steered direction; instead taking a wider trajectory through the turn than the driver intended. The loss of traction can be detected by sensing the lateral acceleration of each tire with the ATMS 18, and using it to calculate the tire's lateral force. The absolute value of the lateral force where oversteer/understeer will occur will vary depending upon road conditions, tread wear, and other factors. However, the tires will display a characteristic increase in lateral force on all four tires during the turn, followed by a rapid decrease in lateral forces in either the front (understeer) or rear (oversteer) tires. In one example, the lateral forces are monitored at all four vehicles tires, and examined for characteristic lateral force profiles. In addition, the steering wheel angle and vehicle speed can be used as inputs to the detection scheme to increase robustness. When oversteer/understeer is detected, the condition can be mitigated by pulsing the brakes rapidly at all four tires, or by pulsing the brakes at selective tires.

Referring to FIG. 13, in step 500, tire signals are generated at each of the vehicle wheels, which are indicative of the lateral acceleration experienced in each tire of the vehicle. From the lateral acceleration data, a lateral tire force (LF) for each tire is determined in step 502. This can be accomplished by any conventional lateral tire force determination. The lateral tire force profiles for the front tires are examined in step 504. If a sudden drop in lateral force is detected for the front tires only, an understeer condition is declared. Otherwise, the lateral tire forces for the rear tires are examined in step 506. Again, if a sudden drop in lateral force is detected for the rear tires only, an oversteer condition is declared. If either an understeer or oversteer condition exists, appropriate braking actions can be carried out in step 508. This may include braking at all of the tires, or select tires.

As in the previous routines, the oversteer/understeer condition can be broadcast to other vehicle subsystems. This may include safety modules such as the active/passive safety systems, ABS, RSC, or integrated vehicle dynamics controller. By broadcasting the oversteer/understeer condition, these other systems can then optimize their performance based upon the oversteer/understeer. For instance, if a rollover event is declared, the thresholds that are used in activating or initiating interventions may be adjusted, scaled, opened, or relaxed, to alter intervention timing because of the oversteer/understeer. In another example of broadcasting, a pre-arm signal for safety-related countermeasures based upon the tire data may be generated. Pre-arming would be appropriate for the roll stability control system as well as the restraints control system. The brake pressure applied during any intervention or countermeasure may also be modified as a result of the oversteer/understeer, as discussed above with regard to FIG. 5.

The above tasks may be performed via any one or more of the herein mentioned controllers, control systems, stability control systems, or the like. The above-described steps are meant to be illustrative examples; the steps may be performed sequentially, synchronously, simultaneously, or in a different order depending upon the application.

While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Specifically, any of the foregoing loose wheel detection, tire abnormality detection, roadway departure detection, and oversteer/understeer detection can be combined in complementary ways to improve overall vehicle safety, and further enhance existing safety systems such as stability control systems. Accordingly, it is intended that the invention be limited only in terms of the appended claims. 

1. A safety system for a vehicle comprising: a tire sensor located within each wheel of the vehicle and each generating a tire signal comprising pressure, temperature and multi-axis acceleration data; at least one vehicle dynamics sensor providing a vehicle dynamics signal; and a controller communicating with each tire sensor and the at least one vehicle dynamics sensor, the controller, in response to the vehicle dynamics signal; generating a tire abnormal state value as a function of the multi-axis acceleration data of the tire signal and a comparison of frequency response characteristics of the tire signal; and transmitting the tire abnormal state to at least one vehicle system controller.
 2. A system according to claim 1 wherein the controller generates the tire abnormal state value as a function of the tire signal by comparing frequency response characteristics of the tire signal to stored frequency response characteristics indicative of different tire abnormalities.
 3. A system according to claim 2 wherein the controller further generates the tire abnormal state value as a function of the tire signal by comparing frequency response characteristics of one of the tire signals to frequency response characteristics of at least two other tire signals.
 4. A system according to claim 2, wherein the tire abnormal state value is a loose wheel value.
 5. A system according to claim 4 wherein the controller further generates the loose wheel value as a function of the tire signal by comparing amplitude response characteristics of the tire signal to stored amplitude response characteristics indicative of a loose wheel condition.
 6. A system according to claim 3 wherein the controller further generates the loose wheel value as a function of the tire signal by comparing frequency response characteristics of one of the tire signals to frequency response characteristics of at least two other tire signals.
 7. A system according to claim 1 wherein the controller generates the tire abnormal state value as a function of the tire signal by comparing frequency response characteristics of one of the tire signals to frequency response characteristics of at least two other tire signals.
 8. A system according to claim 7, wherein the tire abnormal state value is a loose wheel value.
 9. A system according to claim 1 wherein the controller communicates with each tire sensor by wireless transmission.
 10. A system according to claim 1 further comprising an indicator for signaling the tire abnormal state value.
 11. A system according to claim 1 wherein the at least one vehicle dynamics sensor comprises a vehicle speed sensor and a braking sensor.
 12. A system according to claim 1 wherein the at least one vehicle system controller comprises a stability control system.
 13. A system according to claim 12 wherein the stability control system is adapted to modify stability control parameters in response to the tire abnormal state value.
 14. A system according to claim 1 wherein the controller communication with each tire sensor also generates a roadway departure signal as a function of the multi-axis acceleration data of the tire signals and transmits the roadway departure signal to at least one vehicle system controller.
 15. A system according to claim 14 wherein the controller generates the roadway departure signal as a function of the tire signals by comparing frequency and amplitude response characteristics of the tire signal to stored frequency and amplitude response characteristics indicative of different roadway surfaces.
 16. A system according to claim 15 wherein the controller also generates a lateral tire force signal for each of the vehicle wheels as a function of the respective multi-axis acceleration data of the tire signal, generates an oversteer/understeer signal as a function of the lateral tire force signals, and transmits the brake signal to the brake system in response to the oversteer/understeer signal.
 17. A system according to claim 16 wherein the controller generates the oversteer signal by detecting a sudden drop in lateral tire forces for both of the rear tires, in the presence of lateral tire forces in the same direction on the front tires.
 18. A system according to claim 16 wherein the controller generates the understeer signal by detecting a sudden drop in lateral tire forces for both of the front tires, in the presence of lateral tire forces in the same direction on the rear tires.
 19. A system according to claim 16 wherein the vehicle dynamics signal comprises a vehicle speed signal and a steering wheel angle signal.
 20. A system according to claim 14 wherein the controller generates the roadway departure signal as a function of the tire signals by comparing frequency response characteristics of the left tire signals to frequency response characteristics of the right tire signals.
 21. A system according to claim 14 wherein the at least one vehicle system controller comprises a stability control system.
 22. A system according to claim 21 wherein the stability control system is adapted to modify stability control parameters in response to the roadway departure signal.
 23. A safety system for a vehicle comprising: a tire sensor located within each wheel of the vehicle and generating a tire signal comprising pressure, temperature and multi-axis acceleration data; at least one vehicle dynamics sensor providing a vehicle dynamics signal; and a controller communicating with each tire sensor and the at least one vehicle dynamics sensor, the controller, in response to the vehicle dynamics signal, generating a roadway departure signal as a function of the multi-axis acceleration data of the tire signals as a comparison of frequency and amplitude response characteristics of the tire signal; and transmitting the roadway departure signal to at least one vehicle system controller.
 24. A system according to claim 23 wherein the controller generates the roadway departure signal as a function of the tire signals by comparing frequency and amplitude response characteristics of the tire signal to stored frequency and amplitude response characteristics indicative of different roadway surfaces.
 25. A system according to claim 23 wherein the controller generates the roadway departure signal as a function of the tire signals by comparing frequency response characteristics of the left tire signals to frequency response characteristics of the right tire signals.
 26. A system according to claim 23 wherein the at least one vehicle system controller comprises a stability control system.
 27. A system according to claim 26 wherein the stability control system is adapted to modify stability control parameters in response to the roadway departure signal.
 28. A safety system for a vehicle comprising: a tire sensor located within each wheel of the vehicle and generating a tire signal comprising pressure, temperature and multi-axis acceleration data; at least one vehicle dynamics sensor providing a vehicle dynamics signal; a brake system for applying a braking torque to each of the vehicle wheels in response to a brake signal; and a controller communicating with each tire sensor and the at least one vehicle dynamics sensor, the controller, in response to the vehicle dynamics signal, generating a lateral tire force signal for each of the vehicle wheels as a function of the respective multi-axis acceleration data of the tire signal as a comparison of frequency response characteristics of the tire signal, generating an oversteer/understeer signal as a function of the lateral tire force signal, and transmitting the brake signal to the brake system in response to the oversteer/understeer signal.
 29. A system according to claim 28 wherein the controller generates the oversteer signal by detecting a sudden drop in lateral tire forces for both of the rear tires, in the presence of lateral tire forces in the same direction on the front tires.
 30. A system according to claim 28 wherein the controller generates the understeer signal by detecting a sudden drop in lateral tire forces for both of the front tires, in the presence of lateral tire forces in the same direction on the rear tires.
 31. A system according to claim 28 wherein the vehicle dynamics signal comprises a vehicle speed signal and a steering wheel angle signal. 